Polypeptide multilayer films and methods

ABSTRACT

Polypeptide multilayer films comprising a hydrophobic designed polypeptide, methods of making the polypeptide multilayer films, and methods of designing the hydrophobic polypeptide are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application 60/729,828 filed Oct. 25, 2005, which is incorporated by reference herein.

BACKGROUND

The present invention is directed to polypeptide multilayer films, methods of making the polypeptide multilayer films, and methods of designing the polypeptides.

Polyelectrolyte multilayer films are thin films (e.g., a few nanometers to millimeters thick) composed of alternating layers of oppositely charged polyelectrolytes. Such films can be formed by layer-by-layer assembly on a suitable substrate. In electrostatic layer-by-layer self-assembly (“ELBL”), the physical basis of association of polyelectrolytes is electrostatics. Film buildup is possible because the sign of the surface charge density of the film reverses on deposition of successive layers. The general principle of ELBL deposition of oppositely charged polyions is illustrated in FIG. 1. The generality and relative simplicity of the ELBL film process permits the deposition of many different types of polyelectrolytes onto many different types of surface. Polypeptide multilayer films are a subset of polyelectrolyte multilayer films, comprising at least one layer comprising a charged polypeptide. A key advantage of polypeptide multilayer films is environmental benignity. ELBL films can also be used for encapsulation. Applications of polypeptide films and microcapsules include, for example, nano-reactors, biosensors, artificial cells, and drug delivery vehicles.

The design principles for hydrophilic polypeptides suitable for electrostatic layer-by-layer deposition in a high dielectric constant solvent, e.g., aqueous solution, are elucidated in U.S. Patent Publication No. 2005/0069950, incorporated herein by reference. In brief, the suitability of a polypeptide for ELBL is related to the net charge on the polypeptide and the length of the polypeptide. Polypeptides having the appropriate length and charge properties can readily be deposited to form one or more layers of a polypeptide multilayer film. In particular, for ELBL from high dielectric constant solvents, U.S. Patent Publication No. 2005/0069950 discloses that a hydrophilic polypeptide suitable for ELBL from a high dielectric constant solvent preferably comprises one or more hydrophilic amino acid sequence motifs, that is, contiguous amino acid sequences having a length of about 5 to about 15 amino acid residues and having a linear charge density such that the magnitude of the net charge per residue of an amino acid sequence motif is at least 0.5. A polypeptide for ELBL can be designed in different ways, for example, by joining a plurality of amino acid sequence motifs to each other, either directly or by a linker. Additional design concerns disclosed in U.S. Patent Publication No. 2005/0069950 for designed polypeptides suitable for ELBL include the physical structure of the polypeptides, the physical stability of the films formed from the polypeptides, and the biocompatibility and bioactivity of the films and the constituent polypeptides.

U.S. Patent Publication No. 2005/0069950 discloses polypeptide multilayer films prepared from polypeptides dissolved in aqueous solvent and deposited into a polypeptide multilayer film. Such peptides have a high average charge per unit length to be soluble and monomeric in an aqueous medium. Water is a polar solvent, having a high dielectric constant of 78.4 at 25° C. In general, polypeptides of high net charge density are soluble in water and other polar solvents.

Hydrophobic polyelectrolytes can be used to control the surface tension and viscosity of an aqueous solution. Such polymers aggregate in water, and aggregation is enhanced by increasing the ionic strength; salt screens electrostatic repulsion between chains.

There is a need in the market for a general platform for controlled preparation of biodegradable coatings that are fabricated and stable in non-aqueous environments, e.g., solvents of low dielectric constant.

SUMMARY

Disclosed herein is a multilayer film. In one embodiment, a multilayer film comprises a plurality of layers of polyelectrolytes, the layers comprising alternating oppositely charged polyelectrolytes, wherein a first layer comprises a hydrophobic designed polypeptide, wherein the hydrophobic designed polypeptide comprises one or more hydrophobic amino acid sequence motifs, a length of greater than or equal to 15 amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7. The one or more hydrophobic amino acid sequence motifs comprises length n, at least one nonpolar amino acid residue, and a magnitude of a net charge per residue less than 0.4 but greater than 1/n, wherein n is 5 to 15. A second layer comprises a second layer polyelectrolyte having a charge opposite that of the hydrophobic designed polypeptide.

A method of making a multilayer film is also disclosed herein. In one embodiment, a method of making a film comprises depositing a first layer polyelectrolyte on a surface of a substrate to form a first layer; and depositing a second layer polyelectrolyte on the first layer polyelectrolyte to form a second layer; wherein the first layer polyelectrolyte, the second layer polyelectrolyte, or both, comprises a hydrophobic designed polypeptide; and wherein the first layer polyelectrolyte and the second layer polyelectrolyte have net charges of opposite polarity. The hydrophobic designed polypeptide comprises a hydrophobic amino acid sequence motif, a length of greater than or equal to 15 amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7. The hydrophobic amino acid sequence motif comprises length n, at least one nonpolar amino acid residue, and a magnitude of a net charge per residue less than 0.4 but greater than 1/n, wherein n is 5 to 15.

In another embodiment, a method for identifying a hydrophobic amino acid sequence motif comprises locating a starter amino acid in a first amino acid sequence; examining a second amino acid sequence comprising the starter amino acid and a following n−1 amino acids in the first amino acid sequence for occurrences of positive and negative charges at pH 7; and identifying the second amino acid sequence as a hydrophobic amino acid sequence motif if a magnitude of a net charge per residue of the second amino acid sequence is at least 1/n and less than 0.4; or discarding the second amino acid sequence if the magnitude of the net charge of the second amino acid sequence is less than 1/n or greater than or equal to 0.4, wherein n is 5 to 15.

In another embodiment, a method of designing a hydrophobic designed polypeptide comprises identifying a hydrophobic amino acid sequence motif comprising n amino acids, wherein a magnitude of a net charge per residue of the hydrophobic amino acid sequence is at least 1/n and less than 0.4, and wherein n is 5 to 15; and covalently joining two or more hydrophobic amino acid sequence motifs; wherein the two or more hydrophobic amino acid sequence motifs are the same or different.

These and other embodiments, advantages and features of the invention become clear when detailed description and examples are provided in subsequent sections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of the assembly of oppositely charged polypeptides.

DETAILED DESCRIPTION

Disclosed herein are multilayer films comprising a hydrophobic designed polypeptide, methods of making the multilayer films comprising a hydrophobic designed polypeptide and methods of designing a hydrophobic designed polypeptide. Also disclosed are a method of identifying a hydrophobic amino acid sequence motif from known amino acid sequence data and a method of designing a hydrophobic amino acid sequence motif de novo.

A multilayer film comprising a hydrophobic designed polypeptide is useful for a variety of purposes, e.g., fabrication of environmentally benign anisotropic films. Such films are useful for a variety of purposes, e.g., coating optical devices and waveguides, connecting micro-sized circuits, and making liquid crystal displays. Thin films of water on the surface of antennas, radomes or feed waveguides can cause large attenuation of transmitted or received signals. A hydrophobic coating on such devices can be useful in limiting such signal attenuation.

The hydrophobic designed polypeptide can be fabricated into a multilayer film by electrostatic layer-by-layer assembly by deposition, spraying, or another suitable method using a solution of the hydrophobic designed polypeptide in a low dielectric constant solvent.

As used herein, “layer” means a thickness increment, e.g., on a substrate for film formation, following an adsorption step. “Multilayer” means multiple (i.e., two or more) thickness increments. A “polyelectrolyte multilayer film” is a film comprising two or more thickness increments of polyelectrolytes. After deposition, the layers of a multilayer film may not remain as discrete layers. In fact, it is possible that there is significant intermingling of species, particularly at the interfaces of the thickness increments.

The term “polyelectrolyte” includes polycationic and polyanionic materials having a molecular weight of greater than 1,000. Additionally, polyelectrolytes for use in high dielectric constant solvents comprise at least 5 charges per molecule. Suitable polyelectrolyte materials for multilayer film assembly in a low dielectric constant solvent include, for example, hydrophobic polyelectrolytes. Some examples of hydrophobic polyelectrolytes are styrene-maleic anhydride (SMA), styrene acrylates (SA), alkylated urethane copolymers, and certain emulsion products having chemistries related to SMA or SA.

“Amino acid” means a building block of a polypeptide. As used herein, “amino acid” includes the 20 common naturally occurring L-amino acids, all other natural amino acids, all non-natural amino acids, and all amino acid mimics, e.g., peptoids.

“Naturally occurring amino acids,” means the 20 common naturally occurring L-amino acids, that is, glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, aspartic acid, asparagine, glutamic acid, glutamine, arginine, lysine, histidine, phenylalanine, tyrosine, tryptophan, and proline.

“Non-natural amino acid” means an amino acid other than any of the 20 common naturally occurring L-amino acids. A non-natural amino acid can have either L- or D-stereochemistry.

“Peptoid,” or N-substituted glycine, means an analog of the corresponding amino acid monomer, with the same side chain as the corresponding amino acid but with the side chain appended to the nitrogen atom of the amino group rather than to the α-carbons of the residue. Consequently, the chemical linkages between monomers in a polypeptoid are not peptide bonds, which can be useful for limiting proteolytic digestion.

“Amino acid sequence” and “sequence” mean a contiguous length of polypeptide chain that is at least two amino acid residues long.

“Residue” means an amino acid in a polymer or oligomer; it is the residue of the amino acid monomer from which the polymer was formed. Polypeptide synthesis involves dehydration, that is, a single water molecule is “lost” on addition of the amino acid to a polypeptide chain.

“Amino acid sequence motif” means a contiguous amino acid sequence comprising n amino acid residues, wherein n is 5 to 15.

“Hydrophilic amino acid sequence motif” means an amino acid sequence motif for which the magnitude of the net charge per residue of an amino acid sequence motif is at least 0.4; specifically, the magnitude of the net charge per residue is at least 0.5. As used herein, the magnitude of the net charge refers to the absolute value of the net charge, that is, the net charge can be positive of negative.

“Hydrophobic amino acid sequence motif” means an amino acid sequence motif of length n comprising at least one nonpolar amino acid residue and for which the magnitude of the net charge per residue of the amino acid sequence motif is less than 0.4 but greater than 1/n. In one embodiment, the magnitude of the net charge per residue of the hydrophobic designed polypeptide is less than 0.25 at pH 7.

“Designed polypeptide,” means a polypeptide designed for use in fabrication of a polypeptide multilayer film. A designed polypeptide comprises one or more amino acid sequence motifs, wherein the polypeptide is at least 15 amino acid residues long. A practical upper limit on the length is 1,000 amino acid residues. For a designed polypeptide comprising more than one amino acid sequence motif, the amino acid sequence motifs are covalently joined together, either directly or by a linker. A designed polypeptide can comprise multiple copies of identical amino acid sequence motifs or multiple different amino acid sequence motifs.

“Hydrophilic designed polypeptide” means a polypeptide comprising one or more hydrophilic amino acid sequence motifs, wherein the polypeptide is at least 15 amino acid residues in length and the ratio of the number of charged residues of the same polarity minus the number of residues of the opposite polarity to the total number of residues in the polypeptide is greater than or equal to 0.4 at pH 7. In other words, the magnitude of the net charge per residue of the polypeptide is greater than or equal to 0.4. In one embodiment, the ratio of the number of charged residues of the same polarity minus the number of residues of the opposite polarity to the total number of residues in the polypeptide is greater than or equal to 0.5 at pH 7. In other words, the magnitude of the net charge per residue of the polypeptide is greater than or equal to 0.5.

“Hydrophobic designed polypeptide” means a polypeptide comprising one or more hydrophobic amino acid sequence motifs, wherein the polypeptide is at least 15 amino acid residues in length and the magnitude of the net charge per residue of the polypeptide is less than 0.4 at pH 7. In some embodiments, the length of the hydrophobic designed polypeptide is greater than 18, 20, 25, 30, 32, or 35 amino acid residues.

A “high dielectric constant solvent” means a solvent with a dielectric constant greater than or equal to 50 under the conditions used to prepare the multilayer film. For example, the dielectric constant of water at 25° C. is 78.4.

A “low dielectric constant solvent” means a solvent with a dielectric constant less than 50 under the conditions used to prepare the multilayer film. For example, the dielectric constant of dimethyl sulfoxide (DMSO) at 20° C. is 48.9. Low dielectric constant solvents suitable for preparation of a hydrophobic multilayer film include DMSO, acetonitrile, trifluoroacetic acid, N,N-dimethylformamide, ethanol, and methanol. A mixture of solvents (for example, a mixture of acetonitrile and toluene) resulting in a low dielectric constant for the mixture is also considered a low dielectric constant solvent.

“Primary structure” means the contiguous linear sequence of amino acids in a polypeptide chain, and “secondary structure” means the more or less regular types of structure in a polypeptide chain stabilized by non-covalent interactions, usually hydrogen bonds. Examples of secondary structure include α helix, β sheet, and β turn.

“Polypeptide multilayer film” means a film comprising one or more designed polypeptides, wherein the designed polypeptides are hydrophilic, hydrophobic, or a combination thereof. In some instances, the polypeptide multilayer film comprises, in addition to the designed polypeptide, another type of polyelectrolyte in one or more layers, for instance a chemically modified polypeptide, a nonbiological organic polyelectrolyte, or a polysaccharide. For example, a polypeptide multilayer film can comprise a first layer comprising a designed polypeptide and a second layer comprising a polyelectrolyte have a net charge of opposite polarity to the designed polypeptide. The second layer can be another designed polypeptide or another polyelectrolyte. If the first layer has a net positive charge, the second layer has a net negative charge; and if the first layer has a net negative charge, the second layer has a net positive charge.

“Substrate” means a solid material with a suitable surface for adsorption of polyelectrolytes from a solution in either a high dielectric constant solvent or a low dielectric constant solvent. The surface of a substrate can have essentially any shape, for example, planar, spherical, rod-shaped, etc. A substrate surface can be regular or irregular. A substrate can be a crystal. Substrates range in size from the nanoscale to the macro-scale. Moreover, a substrate optionally comprises several small sub-particles. A substrate can be made of organic material, inorganic material, bioactive material, or a combination thereof. Nonlimiting examples of substrates suitable for adsorption of hydrophobic polypeptides from a low dielectric constant solvent include silicon wafers; silicone; surfaces treated with an alkylsilane; surfaces treated with ESSCOLAM 10™ and other proprietary coatings; organic polymer lattices, e.g., polystyrene or styrene copolymer lattices; and hydrophobic membranes, e.g., nitrocellulose filters.

When a substrate is disintegrated or otherwise removed during or after film formation, it is called “a template” (for film formation). Template particles can be dissolved in appropriate solvents or removed by thermal treatment. If, for example, partially cross-linked melamine-formaldehyde template particles are used, the template can be disintegrated by mild chemical methods, e.g., in DMSO, or by a change in pH value. After dissolution of the template particles, hollow multilayer shells remain which are composed of alternating polyelectrolyte layers.

The present invention provides polypeptide multilayer films, wherein at least one layer of the film comprises a hydrophobic designed polypeptide. Other layers comprise designed hydrophilic polypeptides or other polycations or polyanions.

As described above, a hydrophobic designed polypeptide means a polypeptide comprising one or more hydrophobic amino acid sequence motifs, wherein the polypeptide is at least 15 amino acid residues in length, and the magnitude of the net charge per residue of the polypeptide is less than 0.4 at pH 7. For a hydrophobic designed polypeptide comprising more than one hydrophobic amino acid sequence motif, the hydrophobic amino acid sequence motifs are covalently joined together, either directly or by a linker. A preferred characteristic for a linker is that it disfavors formation of secondary structure across two adjacent amino acid sequence motifs. One example of a suitable linker comprises one to four residues of amino acids known to have negligible tendencies to form secondary structures, for example glycine or proline. In some embodiments, the length of the hydrophobic designed polypeptide is greater than 18, 20, 25, 30, 32 or 35 amino acid residues.

A hydrophobic designed polypeptide comprises a single given hydrophobic amino acid sequence motif, it comprises multiple copies of a single given hydrophobic amino acid sequence motif or it comprises multiple hydrophobic amino acid sequence motifs, each chosen to impart to the hydrophobic designed polypeptide particular desired physical, chemical, or biological properties.

Optionally, a hydrophobic designed polypeptide comprises a label for ease of detection or concentration determination. Examples of suitable labels are tyrosine, a fluorophore, a fluorescently labeled amino acid, a biotinylated amino acid, and the like. The label can be placed at any suitable position in the sequence of the hydrophobic designed polypeptide.

Further, a hydrophobic designed polypeptide optionally comprises a moiety that can form a crosslink between two layers or within a layer of a film comprising the polypeptide. Examples of a crosslinking moiety are the amino acid cysteine and its peptoid analog. The crosslinking moiety is, for example, incorporated into the sequence of a hydrophobic amino acid sequence motif in the hydrophobic designed polypeptide.

A hydrophobic amino acid sequence motif means an amino acid sequence motif (i.e., a contiguous amino acid sequence comprising n amino acid residues, wherein n is 5 to 15) comprising at least one nonpolar amino acid residue and for which the magnitude of the net charge per residue of the amino acid sequence motif is at least 1/n and less than 0.4 at pH 7. Hydrophobic amino acid sequence motifs can include polar, uncharged amino acid residues. A hydrophobic amino acid motif can comprise a mixture of amino acid residues of opposite charge as long as the magnitude of the net charge of the motif meets the specified criterion.

In an embodiment, a hydrophobic amino acid sequence motif has an average per residue hydropathy greater than 0, as calculated with the standard values of Kyte and Doolittle (Kyte, J.; Doolittle, R. J. Mol. Biol. 1982, 157, 105-132).

In an embodiment, a hydrophobic amino acid sequence motif has solubility at 25° C. of less than 50 μg/mL in water or other high dielectric constant solvent and solubility at 25° C. greater than 50 μg/mL in a solvent with a low dielectric constant.

In one exemplary embodiment, a hydrophobic amino acid sequence motif comprises 7 amino acid residues. The hydrophobic amino acid sequence motif has a net charge at pH 7, either positive or negative. The maximum magnitude of the net charge at pH 7 for a motif size of 7 is less than 0.4*7 (<3), while the minimum magnitude of the net charge at pH 7 for a motif size of 7 is at least 1/7. The maximum number of charged amino acids, of any polarity, for a motif size of 7 is about 4, and the minimum number of nonpolar amino acids for a motif size of 7 is at least 1.

The naturally occurring amino acids having nonpolar side chains include: alanine, cysteine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan, tyrosine, and valine. Nonpolar side chains consist mainly of hydrocarbon. Any functional groups they contain are uncharged at pH 7 and are incapable of participating in hydrogen bonding.

The naturally occurring amino acids with polar side chains are arginine, asparagine, aspartic acid (or aspartate), glutamine, glutamic acid (or glutamate), histidine, lysine, serine, and threonine. Polar side chains contain functional groups that are either charged at pH 7 or that are able to participate in hydrogen bonding.

The naturally occurring amino acids with positively-charged (basic) side chains at pH 7 are arginine (Arg), histidine (His), and lysine (Lys). The naturally occurring amino acid residues with negatively-charged (acidic) side chains at pH 7 are glutamic acid (or glutamate) (Glu) and aspartic acid (or aspartate) (Asp).

Also provided is a method for identifying a hydrophobic amino acid sequence motif from the genomic or proteomic information of a specific organism, such as the human genome. For example, the primary structure of complement C3 (gi|68766) or lactotransferrin (gi|4505043) can be used to search for hydrophobic amino acid sequence motifs that might be present in the amino acid sequence.

The method comprises selecting a starter amino acid residue in a first amino acid sequence; examining a second amino acid sequence comprising the starter amino acid residue and the following n−1 amino acid residues in the first amino acid sequence for occurrences of positive and negative charges, wherein n is 5 to 15; and identifying the second amino acid sequence as a hydrophobic amino acid sequence motif if the magnitude of the net charge of the side chains of the n amino acid residues at pH 7 is less than 0.4*n but greater than 1/n; or discarding the second amino acid sequence if the magnitude of the net charge of the side chains of the n amino acid residues at pH 7 is greater than or equal to 0.4*n. The method can further comprise determining the net charge of the side chains of the n amino acid residues of the second amino acid sequence. If the second amino acid sequence is discarded, a new search can begin at another amino acid in the first amino acid sequence.

The invention also provides a method for de novo design of a hydrophobic amino acid sequence motif.

De novo design of a hydrophobic amino acid sequence motif follows essentially similar rules, except that a hydrophobic amino acid sequence motif designed de novo is not limited to amino acids found in nature. A length of motif n and a desired sign and magnitude of net charge are chosen. Then, n amino acids are selected for the amino acid sequence motif that result in the desired sign and magnitude of charge, so that the magnitude of the net charge of the n amino acids is at least 1/n but less than 0.4*n.

A potential advantage of de novo design of an amino acid sequence motif is that the practitioner can select from among all amino acids (the 20 naturally occurring ones and all non-natural amino acids) to achieve the desired net charge, rather than being limited to the amino acids found in a particular known protein sequence. The larger pool of amino acids enlarges the potential range of physical, chemical and/or biological characteristics that can be selected in designing the sequence of the motif compared to identification of an amino acid sequence motif in a genomic sequence.

Another aspect of the invention provides a method of designing a hydrophobic designed polypeptide.

The method comprises identifying a hydrophobic amino acid sequence motif comprising n amino acids; and covalently joining two or more hydrophobic amino acid sequence motifs, wherein the two or more hydrophobic amino acid sequence motifs are the same or different.

In some cases, a design concern regarding hydrophobic amino acid sequence motifs and hydrophobic designed polypeptides is their propensity to form secondary structures, notably α helix or β sheet. In some embodiments, it is desirable to be able to control, e.g., minimize, secondary structure formation by the designed polypeptides in solution in order to maximize control over multilayer film layer formation. First, it is preferred that sequence motifs be relatively short, that is about 5 to about 15 amino acids, because long motifs are more likely to adopt a stable three-dimensional structure in solution. Second, a linker, such as a glycine or proline residue, covalently joined between successive amino acid sequence motifs in a designed polypeptide will reduce the propensity of the polypeptide to adopt secondary structure in solution. Glycine, for example, has a very low α helix propensity and a very low β sheet propensity, making it energetically very unfavorable for a glycine and its neighboring amino acids to form regular secondary structure in aqueous solution. Third, the α helix and β sheet propensity of the designed polypeptides themselves can be minimized by selecting amino acid sequence motifs for which the summed α-helix propensity is less than 7.5 and the summed β sheet propensity is less than 8. “Summed” propensity means the sum of the α-helix or β-sheet propensities of all amino acids in a motif. Amino acid sequence motifs having a somewhat higher summed α helix propensity and/or summed β sheet propensity are suitable for ELBL, particularly when joined by linkers such as Gly or Pro. In certain applications, the propensity of a polypeptide to form secondary structure can be relatively high as a specific design feature of multilayer film fabrication. The secondary structure propensities for all 20 naturally occurring amino acids can be calculated using the method of Chou and Fasman (see P. Chou and G. Fasman Biochemistry 13:211 (1974), which is incorporated by reference herein in its entirety).

Another design concern is control of the stability of polypeptide multilayer films. Ionic bonds, hydrogen bonds, van der Waals interactions, and hydrophobic interactions contribute to the stability of multilayer films. In addition, covalent disulfide bonds formed between sulfhydryl-containing amino acids in the polypeptides within the same layer or in adjacent layers can increase structural strength. Sulfhydryl-containing amino acids include cysteine and homocysteine. In addition, a sulfhydryl can be added to β-amino acids such as D,L-β-amino-β-cylohexyl propionic acid; D,L-3-aminobutanoic acid; or 5-(methylthio)-3-aminopentanoic acid. Sulfhydryl-containing amino acids can be used to “lock” (bond together) and “unlock” layers of a multilayer polypeptide film by a change in oxidation potential. Also, the incorporation of a sulfhydryl-containing amino acid in a hydrophobic amino acid sequence motif of a hydrophobic designed polypeptide enables the use of relatively short polypeptides in multilayer film fabrication, by virtue of intermolecular disulfide bond formation. Hydrophobic amino acid sequence motifs containing sulfhydryl-containing amino acids may be selected from a library of motifs identified using the methods described below, or designed de novo.

In one embodiment, the designed sulfhydryl-containing polypeptides, whether synthesized chemically or produced in a host organism, are assembled by ELBL in the presence of a reducing agent to prevent premature disulfide bond formation. Following film assembly, the reducing agent is removed and an oxidizing agent is added. In the presence of the oxidizing agent disulfide bonds form between sulfhydryls groups, thereby “locking” together the polypeptides within layers and between layers where thiol groups are present. Suitable reducing agents include dithiothreitol (DTT), 2-mercaptoethanol (2-ME), reduced glutathione, tris(2-carboxyethyl)phosphine hydrochloride (TCEP), and combinations of more than one of these chemicals. Suitable oxidizing agents include oxidized glutathione, tert-butylhydroperoxide (t-BHP), thimerosal, diamide, 5,5′-dithio-bis-(2-nitro-benzoic acid) (DTNB), 4,4′-dithiodipyridine, sodium bromate, hydrogen peroxide, sodium tetrathionate, porphyrindin, sodium orthoiodosobenzoate, and combinations of more than one of these chemicals.

A hydrophobic designed polypeptide comprises one or more hydrophobic amino acid sequence motifs. The same hydrophobic amino acid sequence motif may be repeated, or different hydrophobic amino acid sequence motifs may be joined in designing a hydrophobic designed polypeptide for inclusion in a multilayer film. In one embodiment, the hydrophobic amino acid sequence motifs are covalently joined with no intervening sequence. In another embodiment, a hydrophobic designed polypeptide comprises two or more hydrophobic amino acid sequence motifs covalently joined by a linker. The linker can be amino acid based, e.g., one or more amino acid residues such as glycine or proline, or it can be any other compound suitable for covalently linking two amino acid sequence motifs. In one embodiment, a linker comprises 1-4 amino acid residues, for example, 1-4 glycine and/or proline resides. The linker comprises a suitable length or composition so that the hydrophobic designed polypeptide is maintained at a net charge per residue that is less than 0.4.

A hydrophobic designed polypeptide with amino acid-based linkers is synthesized using methods well known in the art, such as solid phase synthesis and F-moc chemistry, or heterologous expression in bacteria following gene cloning and transformation. Hydrophobic designed polypeptides may be synthesized by a peptide synthesis company, for example, SynPep Corp. (Dublin, Calif.), produced in the laboratory using a peptide synthesizer, or produced by recombinant DNA methods. Any development of novel methods of peptide synthesis could enhance the production of hydrophobic designed polypeptides but would not fundamentally change peptide design as described herein.

The invention further provides a method of making a multilayer polypeptide film comprising a hydrophobic designed polypeptide.

In an embodiment, the method comprises depositing a first layer hydrophobic designed polypeptide on a surface to form a first layer; and depositing a second layer hydrophobic designed polypeptide on the first layer polypeptide to form a second layer; wherein the net charge of the second layer hydrophobic designed polypeptide is opposite in polarity to the net charge of the first layer hydrophobic designed polypeptide; wherein each hydrophobic designed polypeptide comprises one or more hydrophobic amino acid sequence motifs, a length of 15 to 1000 amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7.

In another embodiment, the method comprises depositing a first layer polypeptide on a surface to form a first layer; and depositing a second layer polypeptide on the first layer polypeptide to form a second layer; wherein the first layer polypeptide, the second layer polypeptide, or both, comprises a hydrophobic designed polypeptide; wherein the first layer polypeptide and the second layer polypeptide have net charges of opposite polarity; and wherein the hydrophobic designed polypeptide comprises a hydrophobic amino acid sequence motif, a length of greater than 15 amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7.

In another embodiment, the method comprises depositing a first layer polyelectrolyte on a surface to form a first layer; and depositing a second layer polyelectrolyte on the first layer polyelectrolyte to form a second layer; wherein at least one of the first layer polyelectrolyte and the second layer polyelectrolyte comprises a hydrophobic designed polypeptide; wherein the first layer polyelectrolyte and the second layer polyelectrolyte have net charges of opposite polarity; and wherein the hydrophobic designed polypeptide comprises a hydrophobic amino acid sequence motif, a length of greater than or equal to amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7.

In another embodiment, the method comprises depositing a plurality of layers of oppositely charged polyelectrolytes on a substrate, wherein at least one layer comprises a hydrophobic designed polypeptide.

Polyelectrolytes for deposition are dissolved in a suitable solvent in which the polyelectrolyte has adequate solubility to achieve an appropriate concentration for the deposition solution. For example, for deposition of a hydrophobic designed polypeptide, the hydrophobic designed polypeptide is dissolved in a low dielectric constant solvent and for deposition of a hydrophilic designed polypeptide, the hydrophilic designed polypeptide is dissolved in a high dielectric constant solvent.

Deposition of layers of oppositely charged polypeptides onto a substrate can be performed by any method known in the art. Deposition of layers of oppositely charged polypeptides in solution onto a substrate can be performed at any temperature at which a solution comprising a polypeptide for deposition is liquid. For example, the aqueous deposition solution of a hydrophilic designed polypeptide can be at a temperature from about 0° C. to about 100° C. for the deposition process or the deposition solution of a hydrophobic designed polypeptide in acetonitrile can be at a temperature from about −48° C. to about 81° C.

In some embodiments, the deposition of the polypeptides is by ELBL. Successively deposited layers have opposite net charges. In other embodiments, the deposition on the substrate is by successively spraying solutions of oppositely charged polypeptides. In yet other embodiments, the deposition on the substrate is by simultaneous spraying of solutions of oppositely charged polypeptides, wherein the solvent of the positively charged polypeptide solution and the solvent of the negatively charged polypeptide solution are miscible.

ELBL is one method of making a multilayer thin film from oppositely charged species, deposited in succession on a solid support. The method is simple and versatile. The basic principle of assembly, Coulombic attraction and repulsion, is far more general than the type of adsorbing species or surface area or shape of support. Electrostatics both drives film assembly and limits it. Several layers of material applied in succession create a solid, multilayer coating. Each layer can have a thickness on the order of nanometers, enabling the design and engineering of surfaces and interfaces at the molecular level. The layering process is repetitive and can be automated, important for control over the process and commercialization prospects.

In the ELBL method of forming a multilayer film, the opposing charges of the adjacent layers provide the driving force for assembly. It is not critical that polyelectrolytes in opposing layers have the same net linear charge density, only that opposing layers have opposite charges. One standard film assembly procedure by deposition includes forming solutions of the polyions at a pH at which they are ionized (i.e., pH 4-10), providing a substrate bearing a surface charge, and alternating immersion of the substrate into the charged polyelectrolyte solutions. Washing the substrate subsequent to separation of the substrate and a deposition solution can optionally be performed prior to exposure of the substrate to the next deposition solution of the oppositely charged polypeptide.

Recently, alternatives to the repetitive assembly of layers by immersion of the substrate into deposition solutions have been developed for the fabrication of ionic polymer films. An iterative spraying method of film assembly has been introduced. The use of spin-coaters has also been demonstrated. Continuous and simultaneous spraying of polyanion and polycation solutions onto a vertically oriented charged surface has also been shown to create a uniform film that grows continuously with spraying time. A vertical orientation enables continuous drainage of excess polyion and solvent.

In some embodiments, an oppositely charged polypeptide deposited on the substrate comprises a hydrophilic designed polypeptide. In other embodiments, at least one of the oppositely charged polypeptides comprises poly (L-lysine) (PLL) or poly (L-glutamic acid) (PLGA).

The concentration of polyelectrolyte suitable for deposition of the polyelectrolyte can readily be determined by one of ordinary skill in the art. An exemplary concentration is 0.1 to 10 mg/mL. Typically, the thickness of the layer produced is substantially independent of the solution concentration of the polyelectrolyte during deposition in the stated range. For typical non-polypeptide polyelectrolytes such as poly(acrylic acid) and poly(allylamine hydrochloride), typical layer thicknesses are about 3 to about 5 Å, depending on the ionic strength of solution. Short polyelectrolytes typically form thinner layers than long polyelectrolytes. Regarding film thickness, polyelectrolyte film thickness depends on humidity as well as the number of layers and composition of the film. For example, PLL/PLGA films 50 nm thick shrink to 1.6 nm upon drying with nitrogen. In general, films of 1 nm to 100 nm or more in thickness can be formed depending on the hydration state of the film and the molecular weight of the polyelectrolytes employed in the assembly.

In addition, the number of layers required to form a stable polyelectrolyte multilayer film will depend on the polyelectrolytes in the film. For films comprising only low molecular weight polypeptide layers, a film will typically have 4 or more bilayers of oppositely charged polypeptides. For films comprising high molecular weight polyelectrolytes such as poly(acrylic acid) and poly(allylamine hydrochloride), films comprising a single bilayer of oppositely charged polyelectrolyte can be stable.

The invention is further illustrated by the following nonlimiting examples.

EXAMPLES Example 1 Preparation of a Multilayer Film Comprising Hydrophobic Designed Polypeptides

Two hydrophobic designed polypeptides are chemically synthesized:

P1: (AAKAAAKG)₃AAKAAAKY (SEQ ID NO:1), comprises 3 copies of the hydrophobic sequence motif AAKAAAK (SEQ ID NO:2) and 1 copy of the hydrophobic sequence motif AAKAAAKY (SEQ ID NO:3) covalently linked together by single glycine residues.

N1: (AAEAAAEG)₃AAEAAAEY (SEQ ID NO:4), comprises 3 copies of the hydrophobic sequence motif AAEAAAE (SEQ ID NO:5) and 1 copy of the hydrophobic sequence motif AAEAAAEY (SEQ ID NO:6) covalently linked together by single glycine residues.

A multilayer film comprising the two hydrophobic designed polypeptides is formed at 25° C. by depositing a layer of P1 dissolved in acetonitrile onto a substrate, e.g., a nitrocellulose membrane, having a relatively low surface charge density. The substrate is immersed in the P1 solution for 15 minutes to permit adsorption of P1 to the substrate, and then removed and rinsed in acetonitrile. The substrate is then immersed in a solution of N1 in acetonitrile to permit adsorption of N1 to the substrate. Following adsorption, the substrate is removed from the N1 solution and rinsed with acetonitrile.

Additional layers are deposited in like manner. A total of five layers of P1 and 5 layers of N1 are alternately deposited.

Example 2 Preparation of a Multilayer Film Comprising Hydrophobic Designed Polypeptides and Hydrophilic Designed Polypeptides

Four designed polypeptides are chemically synthesized, two hydrophobic and two hydrophilic.

The two hydrophobic designed polypeptides are P1 and N1, described above in Example 1.

The two hydrophilic designed polypeptide are the following:

P2: (KAKAKAKG)₃KAKAKAKY (SEQ ID NO:7), comprises 3 copies of the hydrophilic sequence motif KAKAKAK (SEQ ID NO:8) and 1 copy of the hydrophilic sequence motif KAKAKAKY (SEQ ID NO:9) covalently linked together by single glycine residues.

N2: (EAEAEAEG)₃EAEAEAEY (SEQ ID NO:10), comprises 3 copies of the hydrophilic sequence motif EAEAEAE (SEQ ID NO:11) and 1 copy of the hydrophilic sequence motif EAEAEAEY (SEQ ID NO:12) covalently linked together by single glycine residues.

A multilayer film comprising the two hydrophobic designed polypeptides and the two hydrophilic designed polypeptides is formed at 25° C. as follows. P1 is dissolved in a low dielectric constant solvent, e.g., acetonitrile. N1 is dissolved in a low dielectric constant solvent. A layer of P1 is deposited onto a substrate having a relatively low surface charge density, e.g., a nitrocellulose membrane. The substrate is immersed in the P1 solution for 15 minutes to permit adsorption of P1 to the substrate, and then removed and rinsed in acetonitrile to remove loosely bound polypeptide. The substrate is then immersed in a solution of N1 in acetonitrile to permit adsorption of N1 to the substrate. Following adsorption, the substrate is removed from the N1 solution and rinsed with acetonitrile to remove loosely bound polypeptide.

Additional layers of hydrophobic peptide are deposited in like manner.

A hydrophobic film is stable in a hydrophilic solvent because hydrophobic polypeptides are insoluble in a hydrophilic solvent.

A hydrophilic film is stable in a hydrophobic solvent because hydrophilic peptides are insoluble in a hydrophobic solvent.

Layers of hydrophilic designed polypeptides are deposited on top of the hydrophobic film at 25° C. as follows. P2 is dissolved in a hydrophilic solvent, e.g., a mixture of water and acetonitrile. N2 is dissolved in a hydrophilic solvent. A layer of P2 is deposited onto the multilayer film surface. The film is immersed in the P2 solution for 15 minutes to permit adsorption of P2 to the surface, and then removed and rinsed in the mixture of water and acetonitrile to remove loosely bound peptide. The substrate is then immersed in a solution of N2 in the mixture of water and acetonitrile to permit adsorption of N2 to the surface. Following adsorption, the film is removed from the N2 solution and rinsed with the mixture of water and acetonitrile to remove loosely bound peptide.

An increasingly hydrophilic film can be built by depositing increasingly hydrophilic polypeptides from an increasingly hydrophilic solvent, e.g., an increasing percentage of water in a water/methanol mixture.

An increasingly hydrophobic film can be built by depositing increasingly hydrophobic polypeptides from an increasingly hydrophobic solvent, e.g., a decreasing percentage of water in a water/methanol mixture.

The use of the terms “a” and “an” and “the” and similar referents (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms first, second etc. as used herein are not meant to denote any particular ordering, but simply for convenience to denote a plurality of, for example, layers. The terms “comprising”, “having”, “including”, and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted. Recitation of ranges of values are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The endpoints of all ranges are included within the range and independently combinable. All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”), is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as used herein.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

1. A multilayer film comprising: a plurality of layers of polyelectrolytes, the layers comprising alternating oppositely charged polyelectrolytes, wherein a first layer comprises a hydrophobic designed polypeptide, wherein the hydrophobic designed polypeptide comprises one or more hydrophobic amino acid sequence motifs, a length of greater than or equal to 15 amino acid residues, and a magnitude of a net charge per residue of less than 0.4 at pH 7, the one or more hydrophobic amino acid sequence motifs comprising length n, at least one nonpolar amino acid residue, and a magnitude of a net charge per residue less than 0.4 but greater than 1/n, wherein n is 5 to 15, and wherein a second layer comprises a second layer polyelectrolyte having a charge opposite that of the hydrophobic designed polypeptide.
 2. The multilayer film of claim 1, wherein the magnitude of the net charge per residue of the hydrophobic designed polypeptide is less than 0.25 at pH
 7. 3. The multilayer film of claim 1, wherein the second layer polyelectrolyte comprises a hydrophilic designed polypeptide comprising one or more hydrophilic amino acid sequence motifs, wherein the one or more hydrophilic amino acid sequence motifs consists of 5 to 15 amino acids and has a magnitude of a net charge per residue of greater than 0.4, wherein the hydrophilic designed polypeptide is at least 15 amino acids long, and has a magnitude of a net charge per residue of greater than 0.4.
 4. The multilayer film of claim 1, wherein the multilayer film is formed on a substrate.
 5. The multilayer film of claim 4, wherein the substrate is a nitrocellulose membrane, a silicon wafer, silicone, a surface treated with an alkylsilane, or an organic polymer lattice.
 6. The multilayer film of claim 1, comprising at least 4 pairs of alternately charged layers.
 7. The multilayer film of claim 1, having a thickness of 1 nm to 100 nm. 8-17. (canceled)
 18. A method for identifying a hydrophobic amino acid sequence motif, comprising locating a starter amino acid in a first amino acid sequence; examining a second amino acid sequence comprising the starter amino acid and a following n−1 amino acids in the first amino acid sequence for occurrences of positive and negative charges at pH 7; and identifying the second amino acid sequence as a hydrophobic amino acid sequence motif if a magnitude of a net charge per residue of the second amino acid sequence is at least 1/n and less than 0.4; or discarding the second amino acid sequence if the magnitude of the net charge of the second amino acid sequence is less than 1/n or greater than or equal to 0.4, wherein n is 5 to
 15. 19. A method of designing a hydrophobic designed polypeptide, comprising identifying a hydrophobic amino acid sequence motif comprising n amino acids, wherein a magnitude of a net charge per residue of the hydrophobic amino acid sequence is at least 1/n and less than 0.4, and wherein n is 5 to 15; and covalently joining two or more hydrophobic amino acid sequence motifs; wherein the two or more hydrophobic amino acid sequence motifs are the same or different.
 20. The multilayer film of claim 1, wherein the hydrophobic designed polypeptide comprises two or more hydrophobic amino sequence motifs joined by 1-4 glycine or proline residues.
 21. The multilayer film of claim 1, wherein the hydrophobic amino acid sequence motif has a solubility at 25° C. of less than 50 μg/mL in water.
 22. The multilayer film of claim 1, wherein the hydrophobic designed polypeptide has a summed α-helix propensity of less than 7.5 and a summed β sheet propensity of less than
 8. 23. The multilayer film of claim 1, wherein the hydrophobic amino acid sequence motif is designed de novo. 